Vision and audition represent the outside world in spatial and temporal synergy that is crucial for guiding nearly all natural activities. The two systems differ dramatically in their processing of space;images are mapped directly onto the retina, while auditory space must be constructed centrally using location- dependent cues based upon interaural differences and spectral content. From these diverse inputs, visual and auditory space must be integrated into a common coordinate scheme and reference frame to be useful. Additionally, eye movements must be tracked accurately to maintain space constancy because they shift the retinal image relative to the head while the ears (and auditory space) remain head-fixed. The goal of this project is to understand how spatial co-calibration between the senses is maintained in humans despite the challenges of development, disease, and aging. Specific aims will: 1) establish the role of eye position in audio-visual interactions underlying spatial localization;2) examine the relative contributions of eye position and cross-sensory experience on adaptive changes in sound localization after prism-induced shifts of visual space;and 3) elucidate novel adaptive mechanisms in sound localization following direct manipulations of auditory spatial cues using "virtual ears." Behavioral experiments before and after adaptive challenges will quantify the accuracy and precision of auditory and visual spatial localization across a broad region of frontal (multi-sensory) space while controlling and monitoring sensory inputs and eye position over time. Influences of senescence on the spatial senses and adaptive plasticity will be addressed into the ninth decade. This project will provide a fundamental understanding of audio-visual integration and adaptive plasticity between the spatial senses. These factors are essential for the recovery of normal spatial behavior following the challenges of disease and natural aging. A next step is to exploit this new knowledge towards the development of novel diagnostic and therapeutic interventions.